Assignment on electric potential and potential energy

Question 1

A charge of 2C is taken from a point where the potential is -20V to point where the potential
is V. If 400 J of work is done in the process, find V.

Ans: 180V

Question 2

Toe point charges of -10μC and +40μC are kept 15 cm apart. At which point on the line
joining them will the electric potential be zero.

Ans: 3 cm from -10μC charge

Question 3

Three point charges Q1=25μC, Q2=50μC Q3=100μC are
kept at the corners A, B and C respectively of an equilateral triangle ABC having each side of 7.5 m.
find the total electrostatic potential energy of the system.

Ans: 10.5 J

Question 4

How much kinetic energy is gained by an electron, initially at rest when it moves through a potential difference
of 1000 V?

Ans: 103eV or 1.6 x 10-16 J

Question 5

Two positive charges of +12μC and +8μC are placed 10 cm apart. Find the work done in bringing them 4 cm
closer.

Ans: 5.7 J

Question 6

A charge of 5μC is placed at a point. What is the work required to carry a charge of 2C at a distance
of 6 cm from it in a circular path around it to the diametrically opposite end?

Ans: Zero

Question 7

An electron is liberated from the lower of the two large parallel metal plates separated by a distance
of 20 mm. The upper plate has a potential of +2400 V relative to the lower plate. How long does the electron take to reach
the upper plate? (e/m = 1.8 x 1011 C/kg)